Shear-activated phase transformations of diborides via machine-learning potential molecular dynamics

SY Lin and D Holec and DG Sangiovanni and T Leiner and L Hultman and PH Mayrhofer and N Koutná, ACTA MATERIALIA, 301, 121606 (2025).

DOI: 10.1016/j.actamat.2025.121606

The layered character of transition metal diborides (TMB2:s)-with three structure polymorphs representing different stackings of the metallic sublattice-evokes the possibility of activating phase-transformation plasticity via mechanical shear strain. This is critical to overcome the most severe limitation of TMB2:s: their brittleness. To understand finite-temperature mechanical response of the a, w, and y polymorphs at the atomic scale, we train machine-learning interatomic potentials (MLIPs) for TMB2:s, TM = (Ti, Ta, W, Re). Validation against ab initio data set supports the MLIPs' capability to predict structural and elastic properties, as well as shear-induced slipping and phase transformations. Nanoscale molecular dynamics simulations (> 10(4 )atoms; approximate to 5(3) nm(3)) allow evaluating theoretical shear strengths attainable in single-crystal TMB2:s and their temperature evolution from 300 up to 1200 K. Quantitative structural analysis via angular and bond-order Steinhardt parameter descriptors shows that (0001)1210 and (0001)1010 shearing activates transformations between the (energetically) metastable and the preferred phase of TiB2, TaB2, and WB2. These transformations can be promoted by additional tensile or compressive strain along the 0001 axis. The preferred phase of ReB(2 )shows negative thermal expansion and an unprecedented shear-induced plasticity mechanism: metallic/boron layer interpenetration and uniform lattice rotation.

Return to Publications page